Moments of weaknesses – exploiting vulnerabilities between germination and encystment in the Phytomyxea

Abstract

Attempts at management of diseases caused by protozoan plant parasitic Phytomyxea have often been ineffective. The dormant life stage is characterised by long‐lived highly robust resting spores that are largely impervious to chemical treatment and environmental stress. This review explores some life stage weaknesses and highlights possible control measures associated with resting spore germination and zoospore taxis. With phytomyxid pathogens of agricultural importance, zoospore release from resting spores is stimulated by plant root exudates. On germination, the zoospores are attracted to host roots by chemoattractant components of root exudates. Both the relatively metabolically inactive resting spore and motile zoospore need to sense the chemical environment to determine the suitability of these germination stimulants or attractants respectively, before they can initiate an appropriate response. Blocking such sensing could inhibit resting spore germination or zoospore taxis. Conversely, the short life span and the vulnerability of zoospores to the environment require them to infect their host within a few hours after release. Identifying a mechanism or conditions that could synchronise resting spore germination in the absence of host plants could lead to diminished pathogen populations in the field.

Enzymatic Investigation of Spongospora subterranea Zoospore Attachment to Roots of Potato Cultivars Resistant or Susceptible to Powdery Scab Disease

“…Infection of plant hosts by zoospores is preceded by a distinct sequence of initial zoospore recognition and attachment. Pathogen reactions to a host can be modelled on this pattern, making it a promising target for disease prevention [ 5 , 6 , 7 ]. Following attachment to a host root, S. subterranea zoospores discharge their contents into the plant cell walls via a particular ‘Rohr’ and ‘Stachel’ structure [ 1 , 8 ].…”

“…Previous studies on other pathosystems suggest that the molecular interactions between host-plant cell-wall surface components and the infective units of pathogens are critical in the management of pathogenesis and plant resistance [ 11 , 12 ]. The initiation of zoospore root attachment has been associated with the production of a range of high- or low-molecular-weight root exudates [ 7 , 13 ] including fucosyl residues [ 14 , 15 ], pectin [ 16 , 17 ], lectins [ 18 ], certain monoclonal antibodies [ 19 ], amino acids [ 20 ] and ions (sodium, strontium and calcium ions) [ 21 ]. Zoospore attachment to host roots by Pythium spp.…”

Development and validation of a novel rapid in vitro assay for determining resistance of potato cultivars to root attachment by Spongospora subterranea zoospores

“…S. subterranea persists in the soil as dormant resting spores (Harrison et al, 1997) that can release motile zoospores under conducive environmental conditions, stimulated by the presence of host plant root exudates (Balendres, Nichols, et al, 2016). Zoospores are attracted by chemotaxis to host roots (Amponsah et al, 2021), to which they attach (encyst) and penetrate through the cell wall, inserting their cellular contents to facilitate infection (Merz, 1997). A multinucleate plasmodium then forms, which segments into uninucleate zoosporangia (Kole, 1954).…”

Large-Scale Protein and Phosphoprotein Profiling to Explore Potato Resistance Mechanisms to Spongospora subterranea Infection

“…Spongospora subterranea is a biotrophic soil inhabiting plant pathogen and one of the most economically significant potato diseases. This pathogen invades both roots and tubers resulting in root disfunction, root galling, and powdery scab lesions on tubers in potato ( Amponsah et al, 2021 ). It has been estimated that tuber infection by S. subterranea accounts for annual losses of A$13.4M in the Australian processing potato sector alone ( Wilson, 2016 ).…”